In particular, the present invention relates to vessels for use in laboratory work at extreme temperatures, which vessels have fluid volumes in the order of up to a few milliliters. Conventional vessels generally are vessels of the screw-threaded closure vessel type and are provided with separate sealing elements such as an O-ring. Such a vessel structure may result in contamination of the contents of the vessel when the material of the O-rings has been damaged by aggressive fluids contents. Furthermore the additional sealing element causes specific production costs.
In a prior art closure vessel assembly the closure is provided with a sealing lip having a shape of an extended parabola in a longitudinal cross-section. At its periphery the sealing lip is provided with a lip sealing surface which is resiliently and sealingly urged against an internal rim of the mouth of the vessel when the closure is in screw-threaded engagement with the vessel. At the internal rim a housing face wall and a housing side wall abruptly merge into each other, i.e. the radius of curvature of the internal rim approximates zero in a longitudinal cross-section. Accordingly, the lip sealing surface is subjected to an annular line contact resulting in substantial surface pressures. Such surface pressures cause the lip seal to be deflected inwardly for a substantial amount when the closure is in screw-threaded engagement with the vessel.
Such sealing structure is not very critical at room temperature. If, however, the vessel is used in a wide range of temperatures of e.g. -136.degree. C. to +100.degree. C., the closure vessel assembly will experience critical conditions during the required closure time. In particular at high temperatures there will be a substantial deformation of the material of the sealing means resulting in a reduction of the sealing forces along with a corresponding leakage of the fluid contents of the vessel. This situation is aggravated by the increase of vapor pressure of the probes at the higher temperatures which may attain 100.degree. C. when the vessel is immersed in a hard water bath. Low temperatures such as -196.degree. C. which are encountered when using liquid nitrogen as a cooling medium result in a plastic deformation of the plastic vessel in particular in the prestressed sealing area. As a result the cooling medium may leak into the vessel and may evaporate causing rupturing of the closure. This may result in environmental contamination.